1997 Apr 02

6

Philips Semiconductors

Product specification

128

PCA8581; PCA8581C

7.3

System configuration

A device generating a message is a ‘transmitter’, a device receiving a message is the ‘receiver’. The device that controls

the message is the ‘master’ and the devices which are controlled by the master are the ‘slaves’.

Fig.5 System configuration.

MBA605

MASTER

TRANSMITTER /

RECEIVER

SLAVE

RECEIVER

SLAVE

TRANSMITTER /

RECEIVER

MASTER

TRANSMITTER

MASTER

TRANSMITTER /

RECEIVER

SDA

SCL

7.4

Acknowledge

The number of data bytes transferred between the start

and stop conditions from transmitter to receiver is

unlimited. Each byte of eight bits is followed by an

acknowledge bit. The acknowledge bit is a HIGH level

signal put on the bus by the transmitter during which time

the master generates an extra acknowledge related clock

pulse. A slave receiver which is addressed must generate

an acknowledge after the reception of each byte. Also a

master receiver must generate an acknowledge after the

reception of each byte that has been clocked out of the

slave transmitter.

The device that acknowledges must pull down the SDA

line during the acknowledge clock pulse, so that the SDA

line is stable LOW during the HIGH period of the

acknowledge related clock pulse (set-up and hold times

must be taken into consideration). A master receiver must

signal an end of data to the transmitter by not generating

an acknowledge on the last byte that has been clocked out

of the slave. In this event the transmitter must leave the

data line HIGH to enable the master to generate a stop

condition.

handbook, full pagewidth

MBA606 - 1

START

condition

S

SCL FROM

MASTER

DATA OUTPUT

BY TRANSMITTER

DATA OUTPUT

BY RECEIVER

clock pulse for

acknowledgement

1

2

8

9